The brain collects the data, files it, cross-references it, creates a baseline for normal. It might be almost impossible to retrieve, but, still, I believe it is there. Nothing is lost.
Anything that deviates from normal is filed closer to the conscious. Hence, Humiliations is easy to access. Likewise the files for Failure, Loss, Disappointment, and Pain. Firsts can also be located near the front of the cabinet, as well as Unusual Moments of Happiness and Joy.
The data from four of our senses slams straight into our memory banks from their positions nearest the brain. This, I think, is why it's harder to remember what something feels like. Touch is too far away. But sight, sound, taste, smell - they're all right there on our heads, bombarding our grey matter in a continuous assault of particles and waves and refracted light.
The scent of a certain kind of plastic and bam! you're in kindergarten wearing a plasticized smock, fingers sticky with paint. A particular song comes on the radio and you're slow dancing under the basketball net with a cute boy in a darkened gymnasium, the air heavy with Drakkar Noir.
I often think in spelling, so running through the alphabet can trigger the information I am looking for. What was that movie? A famous junkie author wrote the book. Burroughs? Close, but no. Jennifer Connelly ass-to-ass. Somewhere in Q-R-S. Requiem for a Dream. Selby. Hubert Selby Jr. And we get there.
Sometimes it takes a while. You set your memory workers a task and then forget about it, but, unbeknownst to your conscious brain, they are digging through the files, they know it's here somewhere, and then, maybe an hour later, eureka! It pops into your head. Our brains are slower than google, but they'll find it eventually. (My brain is slower than others, it often seems.)
In his meditation on a field of daffodils, William Wordsworth wrote, "They flash upon that inward eye." I like that metaphor, but the inward eye is not just visual; it is also auditory, olfactory, gustatory, and tactile, merged somehow with emotions, the flow of our blood through our veins, the complicated way we experience the world.
We might forget, might even want to forget, but nothing is ever lost.